Aluminous material



H. N. BAUMANN, JR., ETAL oct'. 24, 1944.

ALUMINOUS MATERIAL Filed June 10, 1941 trates certain ldrawings, Figure 1 illustrates iication Patented Oct. 24, 1944 y l. gri'.

.UNITED sTATEs PATENT oFElcE ALUMINOUS MATERIAL Henry N. Baumann, Jr., Benner. Niagara Falls, N.

Carborundum Company,

and Raymond C. Y., assignors to The Niagara Falls, N. Y.,

a corporation oi' Delaware 'application .ione 1o, 1941,- serloi No'. 397,490

i 12 Claims.

An abrasive material `has long been made com- `mercially by fusing bauxite or other material having a. high alumina content under reducing conditions in electric furnaces. Alumina of high technical puritysuch as that made by the Bayer process has also been'fused' to produce abrasive material. In both cases the abrasive is chiefly a mineral crystallographically identical with the crystalline form of alumina found in naturelas'corundum. Particular abrasive characteristics of such forms of alpha alumina will.y vary somewhat depending upon the total alumina content, the amount and kind of associated impurities, and the rate of cooling of the sintered product. Under any conditions, however, such products .have certain limitations as regards uniformity, toughness, microstructure, and the degree to which their physical proper-v tiesmay be altered to' lit diiierent abrasive applications. l

'I'he accompanying drawing explains and illusaspects of our invention. In the X-ray back reilection diiraction pattern photograms of powdered aluminous materials; Figure `2 shows the appearance of sintered alpha alumina under high magnification; Figure 3 junder high magnification, of the mass obtained by sinteringtogether, 90% oi' finely divided alu,.-

' mina and 10% T102; and Figure 4 shows the appearance, under high, magnification. of the mass l obtained by sintering together 99% iinely divided alumina and 1% oi' VzOr In our copending application," Serial No. 312,927, iiled January 8, 1940, it has been disclosed that alumina, maybe modified by forming solid solu tions ,with the sesquioxids of either chromium, or

vanadium or with l is the production of alumina grain of considerably increased hardness.

shows the appearance,

both. 'I'he result of this moditemperatures well below the fusion or sintering temperatures of the alumina.

In application Serial No. 312,927 Vit is disclosed that chromium and vanaduim oxides will form solid solutions with alumina by fusion or by a' sintering procedure. Unlike chromium'and vanadium Aoxides however, manganese and iron sesquioxides, when completely fused with aluterns oi.' three diiferent materials.

` mixed with titanium In our copending application, sonal. No.v

357,947, led September 23, 1940, it has been disclosed that alumina may also be modiiied by the formation of solid solutions with the alumina oi ferric oxide, manganese sesquioxide, or mixtures of these two oxides with each other or with e sesquioxides o1' vanadium and chromium at 'gether `90% alumina and mina showing the mina (particularly under reducing conditions) tend to dissociate to a lower oxide state of the typical formula MeO and form aluminates rather than to enter into solid solution. When sintered with alumina however, iron and manganese oxides enter into solid solution in alumina to some extent at or somewhat Ibelow a temperature of 1800 C. 'I'his is shown by Figure 1 which is a representation oi' an X-ray photogram oi back reilection diil'raction powder patthese materials. the powder pattern o f which is indicated in Figure 1 by A, is iinely dividedpure alpha a umina. The second material is a powder obtained by crushing a fusion of 90% alumina snm/10% iron oxide (rezos): the powder pattern. of this material is identiiied in Figure 1 by B. 'I'he third material is "a powder obtainqi by crushing the product formed by sintering to- 10% iron oxide; in oi' this material is Figure 1 theApowder pattern shows that the indicated by C. The photogram uct formed by fusion, are not displaced from the position occupied by the characteristic lines of the pure alumina, thus indicating that in the fused product, no liron oxide entered into solid solution in the" alumina. On the dim-action lines of the sintered iron--oxide-alumina product are appreciably offset from the position of the 4characteristic lines of theA pure' alualumina lattice.

Applicants have discovered that the amount of iron orr manganese oxide which enters into solid solution in alumina during'the sintering process is measurably increased if the oxide is oxide. It has been further discovered that titanium oxide,- presumably of the yformula TizOa, will itself, enter into solid solution in alumina to give products having properties quite similar to thosel resulting from the formation of solid solutions of other metallic oxides, suchas CMQ-V203 vand MnzOs, in alumina. Thus the resulting product, when titanium oxide and ferrlc oxide are used together, contains both oxides in solid solution.

The rst of other hand the presence o f iron in the alpha that both oxides have entered into '1 tion of and describe oxide and mixtures of titanium oxide and i'erric oxide in alumina.

Example I Wnenlfrdm 1-2% of iineiy divided titanium dioxide ifs mixed with 9s-99% of iinely divided alumina and the mixture is sintered to 1800 C. for about two hours, the crystals of the sintered mass, when observed under the petrographic microscope, have slightlydifferent properties from those crystals formed by sintering finely divided alumina alone. Pure ,a1umina crystals are colorless. The crystals .in the sintered mass containing titanium oxide are' in some instances slightly colored to a light pink and may be pleochroic to a reddish purple. The indices of refraction of the crystals inthe sintered mass containing titanium oxide are also somewhat higher than the indices of crystals. Thin sections of the mass of crystals in the sintered product show that the crystals are tightly interlocking and that very little titanium oxide remains as a residual material between the crystals. This fact indicates that probably at least 50% of the TiOz originally used entered in some manner into solid solution in the alumina and caused the difference in optical properties outlined above. At least through some means titanium atoms have entered the alumina lattice.

In preparing the above mixture of materials and other mixtures of alumina and metal oxides for sintering,

solid solution in the alumina in considerable amounts at temperatures much lower than it is possible to use refraction of pure alumina E in particular seem to serve a convenient method is .to mix the v powdered materials with water. and a temporary i binding medium such as dextrin to obtain a workable mass and press the mass under about 2000 psi to form a block or other desired shape. While 1800 C. is in general our preferred temperature, we have successfully sintered articles at both higher and lower temperatures, sorne as 1'700 C. and others as high as 2000 C.

f Example II When 3% of finely divided ferrie oxide is sintered with `97% of finely divided alumina at 1800* C. for about two hours, the crystals of the sintered product show a slight elevation in their indices of refraction over those of pure alumina crystals and are voccasionally colored purple. Ex-

amination under the petrographc microscope reveals that at least 2A; of, the ferric oxide 4used remains as residual material between the crystals indicating that about 1% or vless of ferrie oxide has entered into-solid solution in the alumina. When, however', 2% each of both ferric oxide and titanium oxide are mixed with 96%191 alumina, all in finely divided form, and sintered inthe manner set forth above, examination underj'the petrographic microscope reveals no residual intercrystalline material. It is also indices of refractionof the crystals in the sinnot closely related to in the absence of titanium oxide.

In the copending applications heretofore referred to it has been pointed out that the hardness and the toughness of the alumina may be improved by introducing oxides in solid solution in the alumina and methods are disclosed for varying -these properties by suitable choices of oxides for modifying the alumina and by subsequent treatment.

We have also found that the grain or crystal size .of sintered alumina masses can be varied and controlled by the use of certain oxides in the mixes to be sintered. Thus we have found that the addition of manganese oxide, ferric oxide and other related oxides such as chromium oxide and titanium oxide all of which have similar structures and the metals of which readily assume the trivalent state will, when sintered with alumina, increase the grain size of the crystals in the sintered mass over the size characteristic of pure alumina. -Manganese oxide and titanium oxide as mineralizers, promoting the crystallization of the alumina.

We have found, on the other hand, that oxides ferric oxide and manganese oxide in their general structure or in which the chief valence of the metalis not 3, such as M003, ZrOa, MgO and V205, tend to inhibit crystal growth during the sintering of mixtures of such oxides with alumina. Of these latter oxides, only V205 will, under sintering conditions, undergo a change to a form having a close structural relation to manganese oxide and ferrie oxide.

We have discovered that vanadium oxide in amounts up to about 2% produces a finer grain size while'in larger amounts it has little or no inhibiting effect upon the crystal growth. Other oxides of this growth-inhibiting group produce a refinement of grain size throughout the range of amounts in which -they may usefully be added althoughthe different oxides exhibit their optimum effect at different concentrations. Thus zirconium oxide in amounts from 4-5% is most y effective while molybdenum oxide, though causing d some refinement of grain size when present in found that the A tered mass are appreciably raised and many of the crystals are colored a deep purple :indicating solid solutio in alumina, the ferri'c oxide in virtually twice the amount that it did when used without the titanium oxide. I

'Iitanium oxide has also been found to increase the tendency of other oxides having the same valence and general structure as ferrie oxide to enter into solid solution in alumina. Thus, for example, chromic oxide when admixed with titanium Aoxide and sintered with low percentages, is especially effective in'inhibiting crystal growth when used in amounts of from Pure 18.00 C. fortwo hours develops crystals which upon microscopic examination, prove to have an average diameter of .G25-.030 mm. Figure AII is taken from a photomicrograph (magnification 275K) of a portion of a sintered article of pure alumina.

The effect of zirconium oxide on the grain size of alumina bodies containing it is set forth in the following example:

Ezampze m In the lbody produced by sintering together 1-2% finely 4divided zirconium'oxide and E38-99% finely divided alumina the individual crystals are found to have an average diameter of .01 mm.; in a sintered mass containing of zirconium oxide the average diameterof thebcrystals is .006 mm. When used in larger amounts zirconium oxide produces less markedreduction in size of the crystals in the sintered mass.

The following example illustrates the effect of manganese andtitanium oxides on the ,crystal size of the sintered mass of alumina containing alumina enters into 'I0 these oxides.

finely divided alumina when sintered to titanium oxide and 9999.5% of finely divided alumina at 1800 C. for two hours show an average crystal diameter considerably greater than vthat diameter (.025-.030 sintered alumina.

mm.) characteristic of pure Example V When .52% of 99.5% of finely divided aluminay sintered yas set forth above, crystals of the In the case of `manganese oxide, an average crystal diameter of .08 mm. isA

- formed as a shaped article for sintered mass have an average diameter of .007

mm. When the vanadium oxide is used in somewhat greater amounts, as about 1-2%, the average diameter of the crystals in the sintered mass is still smaller-about .U01-.002 mm. As increasingly larger amounts of vanadium oxide are used, the crystal size of the mass increases until at-a ratio of 8% VzQsf to 92% A1203 the average crystal size is essentially the sintered alumina. Figure IV is taken from a photomicrograph (magnification 275K) of a sintered product containing 1% vanadium oxide.

alumina.

While we do not wish believe that a possible explanation of these but rather remain as flnely'disse'minated particles betwen the alumina grains. It is therefore possible that the oxides of the first mentioned group by entering into solid. solution in the alumina' tend' to promote greater mobility of the valumina molecules thus encouraging the formation oi' larger crystals. In the case of the oxides of the second group, the interstitial particles between the alumina grainsl would have a tendency to reduce diffusion or interchange of -material between the alumina crystals and therefore inhibit crystal growth. l

It is now well recognized that a Wide variety of abrasive media is required for the proper grinding, polishing, or other abrasive working of different materials. It has. been found that by the metho. of the present invention alumina may be m dified by other oxides to produce a very great range of properties in the alumina grain. The properties vaffected by the use oi 45 cgnsisung of Fezo and Mnzot Abrasive grain may be produced according to the present invention by sintering together nely divided alumina and the proper amount of an oxide which wm produce in the alumina the desired characteristics. 'I'he sintered mass may be crushed and screened to produce abrasive granules of useful size. Such abrasive grain is applicable to a number of abrasive uses in both bonded and coated abrasives. Furthermore.. instead of forming abrasive grain, the sintered product containing alumina modified by the oxides in accordance with our invention may be use as such. Articles having great toughness and wear-resistance may be formed by the method of our invention as may also refractory articles.

Where in the specification or in the appended claims we have referred to the oxides, FezOs, MnzOa, CrzOs, TizOa and V203 we have intended these designations to include materials which under the conditions of the process form these oxides or other oxides of the named metals which enter into solid solution in alumina. As pointed out above we vmay simply admix the finely divided oxides with finely divided alumina and form solid solutions or if it is desired to employ soluble salts of the metals a water solution of the salt may be formed and this solution admixed with the alumina particles to be sintered.

When the mixture is dried each alumina particle will be intimately associatedwith a deposit of the metallic salt or compound.

Where percentages are given in this specification or the claims it will be understood that percentages by weight are meant unless it is otherwise specified. y i

While we have set forth herein several examples of ways in which our invention 'may be utilized we do not wish to be limited thereby, butonly by the scope of the appended claims.

We claim:

l. As a new article of manufacture, a sintered product consisting principally of crystallized alumina in which at least one oxide of the group is contained in solid solution, said alumina also containing titanium atoms in thelattice thereof.

2. As a new article of manufacture, abrasive 4 grain consisting -principally of crystals of sintered alumina in which at least one oxide of the group consisting of FezOa and MnzOa is contained in solid solution, said alumina also containing titanium atoms in the lattice thereof.`

3. The method of producing abrasive granules which comprises-mixing together finely divided alumina. titanium dioxide. and at least one oxide of the group consist' g lof F'ezOa` and MmOa, forming the mixture into a dense mass and sintering the mass at a temperature in the range from 1700o C. to 2000 C. whereby a solid solution of' the oxide in the .alumina crystals is produced, and thereafter crushing the sintered mass.

4. An abrasive or wear resistant article'comprising granular crystalline sintered alumina in which at least one oxide of the group consisting of FezOs and MmOa is in solid solution, and which alumina contains titanium in the lattice thereofr and a bond therefor.

5. As a new article of manufacture. a sintered product composed of crystalline alumina containing titanium atoms in the lattice thereof and 203 in s olid solution therein, the alumina com. prising the major portion of the product.

6. As a new article of manufacture, a sintered product composed of' crystalline alumina oon- `prising .the major portion of grain consisting taining titanium atoms in the lattice thereof and MmOi in solid solution therein, the alumina com the product.

article of manufacture, abrasive principally of crystals of sintered alumina in which FeaO.; is contained in solid solution, said alumina also containing titanium atoms ,'LAsanew in the lattice thereof.

thereafter 26 Awhich MnzOa 10. The method of producing abrasive crystals, comprisingy mixing together nely divided alumina, titanium dioxide, and MmOc forming the mixture into a dense mass' and sintering the mass at a temperature in the range from 1700 C. to C. whereby' a solid solution of the oxide in the alumina crystals is produced, and thereafter crushing the sintered mass.

11. An abrasive or wear resistant article comprising granular crystalline sintered alumina in which FezOs is in solid solution, and which alumina contains titanium in the lattice thereof, and a bond therefor.

l2. An abrasive or wear resistant article comprising granular crystalline sintered alumina in is in -solid solution, and which alumina contains titanium in the lattice thereof, and a bond therefor.

Y HENRY N. BAUMANN. JR. RAYMOND C. BENNER. 

